This invention relates to methods of treating insulin-dependent diabetes mellitus, noninsulin-dependent diabetes mellitus, and related conditions and symptoms.
Diabetes mellitus is a condition in which blood glucose levels are abnormally high because the body is unable to produce enough insulin to maintain normal blood glucose levels or is unable to adequately respond to the insulin produced. Insulin-dependent diabetes mellitus (often referred to as type I diabetes) arises when the body produces little or no insulin. About 10% of all diabetics have type I diabetes. Noninsulin-dependent diabetes mellitus (often referred to as type II diabetes) arises when the body cannot adequately respond to the insulin that is produced in response to blood glucose levels. Type II diabetes is often associated with hyperglycemia (high plasma glucose levels due to decreased glucose utilization) and hyperinsulinemia (high plasma insulin levels due to decreased insulin receptors available), factors that contribute to insulin resistance.
Available treatments include weight control, exercise, diet, and drug therapy. Drug therapy for type I diabetes mellitus requires the administration of insulin; however, drug therapy for type II diabetes mellitus usually involves the administration of insulin and/or oral hypoglycemic drugs to lower blood glucose levels. If the oral hypoglycemic drugs fail to control blood sugar, then insulin, either alone or in combination with the hypoglycemic drugs, will usually be administered.
Although many of the symptoms of diabetes mellitus may be controlled by insulin therapy, the long-term complications of both type I and type II diabetes mellitus are severe and may reduce life expectancy by as much as one third. Over time, elevated blood glucose levels damage blood vessels, eyes, kidneys, nerves, autonomic nervous system, skin, connective tissue, and white blood cell function.
Moreover, insulin therapy may result in insulin allergy, insulin resistance, atrophy of the subcutaneous fat at the site of insulin injection (i.e., lipoatrophy), enlargement of subcutaneous fat deposit (i.e., lipohypertrophy) due to lipogenic action of high local concentration of insulin, and insulin adema.
Thus, it would be desirable to find an alternative to the above-described therapies or to administer a drug therapy that may reduce the amount of insulin or hypoglycemic drug required, yet maintain the effectiveness of the insulin or hypoglycemic drug administered.
The present invention provides methods for treating insulin-dependent diabetes mellitus, noninsulin-dependent diabetes mellitus, and related conditions and symptoms. One embodiment includes a method of treating diabetes mellitus in a mammal by administering a therapeutically effective amount of a compound, such as pyridoxal-5xe2x80x2-phosphate, pyridoxal, pyridoxamine, pyridoxine, a 3-acylated pyridoxal analogue, a pharmaceutically acceptable acid addition salt thereof, or a mixture thereof.
In another embodiment, the invention provides a method of treating diabetes mellitus in a mammal by concurrently administering a therapeutically effective amount of a combination of insulin and a compound, such as pyridoxal-5xe2x80x2-phosphate, pyridoxal, pyridoxamine, pyridoxine, a 3-acylated pyridoxal analogue, a pharmaceutically acceptable acid addition salt thereof, or a mixture thereof.
In still another embodiment, the invention provides a method of treating noninsulin-dependent diabetes mellitus in a mammal by concurrently administering a therapeutically effective amount of a combination of a hypoglycemic compound and a compound, such as pyridoxal-5xe2x80x2-phosphate, pyridoxal, pyridoxamine, pyridoxine, a 3-acylated pyridoxal analogue, a pharmaceutically acceptable acid addition salt thereof, or a mixture thereof.
The present invention provides methods for treatment of diabetes mellitus and related conditions and symptoms. Such diabetes mellitus and related conditions include insulin-dependent diabetes mellitus (type I diabetes), noninsulin-dependent diabetes mellitus (type II diabetes), insulin resistance, hyperinsulinemia, and diabetes-induced hypertension. Other diabetes-related conditions include obesity and damage to blood vessels, eyes, kidneys, nerves, autonomic nervous system, skin, connective tissue, and immune system.
In accordance with the present invention, it has been found that compounds, such as, for example, pyridoxal-5xe2x80x2-phosphate, pyridoxal, pyridoxamine, a 3-acylated pyridoxal analogue, a pharmaceutically acceptable acid addition salt thereof, or a mixture thereof, either alone or in combination with insulin and/or hypoglycemic compounds can be used in the treatment of the above-identified diseases and conditions. As used herein, xe2x80x9ctreatmentxe2x80x9d and xe2x80x9ctreatingxe2x80x9d include preventing, inhibiting, and alleviating diabetes mellitus and related conditions and symptoms. In some instances, the treatment may be carried out by administering a therapeutically effective amount of a compound suitable for use in methods of the invention. In other instances, the treatment may be carried out by concurrently administering a therapeutically effective amount of a combination of insulin and a compound suitable for use in methods of the invention. In still other instances, the treatment may involve concurrently administering a therapeutically effective amount of a combination of a hypoglycemic compound and a compound suitable for use in methods of the invention when the diabetes mellitus and related conditions to be treated is type II diabetes, insulin resistance, hyperinsulinemia, diabetes-induced hypertension, obesity, or damage to blood vessels, eyes, kidneys, nerves, autonomic nervous system, skin, connective tissue, or immune system.
A xe2x80x9ctherapeutically effective amountxe2x80x9d as used herein includes a prophylactic amount, for example, an amount effective for preventing or protecting against diabetes mellitus and related conditions and symptoms, and amounts effective for alleviating or healing diabetes mellitus and related conditions and symptoms. Generally, by a administering a compound suitable for use in methods of the invention concurrently with insulin and/or a hypoglycemic compound the insulin and/or hypoglycemic compound may be administered in a dosage amount that is less than the dosage amount required when the insulin and/or hypoglycemic compound is the sole active ingredient. By administering lower dosage amounts of insulin and/or a hypoglycemic compound, the side effects associated therewith should accordingly be reduced and/or the onset of the long-term complications that arise from diabetes mellitus and related conditions may be delayed.
Compounds suitable for use in the methods of the invention include pyridoxal-5xe2x80x2-phosphate, pyridoxal, pyridoxamine, pyridoxine, 3-acylated pyridoxal analogues, pharmaceutically acceptable acid addition salts thereof, or a mixture thereof. 3-Acylated pyridoxal analogues include prodrugs of pyridoxal that provide for slower metabolism to pyridoxal in vivo. For example, one suitable 3-acylated analogue of pyridoxal (2-methyl-3-hydroxy-4-formyl-5-hydroxymethylpyridine) is a compound of the formula I: 
or a pharmaceutically acceptable acid addition salt thereof, wherein
R1 is a straight or branched alkyl group, a straight or branched alkenyl group, in which an alkyl or alkenyl group may be interrupted by a nitrogen or oxygen atom; an alkoxy group; a dialkylamino group; or an unsubstituted or substituted aryl group.
The term xe2x80x9calkylxe2x80x9d group includes a straight or branched saturated aliphatic hydrocarbon chain having from 1 to 8 carbon atoms, such as, for example, methyl, ethyl, propyl, isopropyl (1-methylethyl), butyl, tert-butyl (1,1-dimethylethyl), and the like.
The term xe2x80x9calkenylxe2x80x9d group includes an unsaturated aliphatic hydrocarbon chain having from 2 to 8 carbon atoms, such as, for example, ethenyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-methyl- 1-propenyl, and the like.
The above alkyl or alkenyl groups may optionally be interrupted in the chain by a heteroatom, such as, for example, a nitrogen or oxygen atom, forming an alkylaminoalkyl or alkoxyalkyl group, for example, methylaminoethyl or methoxymethyl, and the like.
The term xe2x80x9calkoxyxe2x80x9d group includes an alkyl group as defined above joined to an oxygen atom having preferably from 1 to 4 carbon atoms in a straight or branched chain, such as, for example, methoxy, ethoxy, propoxy, isopropoxy (1-methylethoxy), butoxy, tert-butoxy (1,1-dimethylethoxy), and the like.
The term xe2x80x9cdialkylaminoxe2x80x9d group includes two alkyl groups as defined above joined to a nitrogen atom, in which the alkyl group has preferably 1 to 4 carbon atoms, such as, for example, dimethylamino, diethylamino, methylethylamino, methylpropylamino, diethylamino, and the like.
The term xe2x80x9carylxe2x80x9d group includes an aromatic hydrocarbon group, including fused aromatic rings, such as, for example, phenyl and naphthyl. Such groups may be unsubstituted or substituted on the aromatic ring by, for example, an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, an amino group, a hydroxy group, or an acetyloxy group.
Preferred R1 groups for compounds of formula I are toluyl or naphthyl. Such R1 groups when joined with a carbonyl group form an acyl group 
which preferred for compounds of formula I include toluoyl or xcex2-naphthoyl. Of the toluoyl group, the p-isomer is more preferred.
Examples of 3-acylated analogues of pyridoxal include, but are not limited to, 2-methyl-3-toluoyloxy-4-formyl-5-hydroxymethylpyridine and 2-methyl-xcex2-naphthoyloxy-4-formyl-5-hydroxymethylpyridine.
Another suitable analogue is a 3-acylated analogue of pyridoxal-4,5-aminal (1-secondary amino-1,3-dihydro-7-hydroxy-6-methylfuro(3,4-c)pyridine) of the formula II: 
or a pharmaceutically acceptable acid addition salt thereof, wherein
R1 is a straight or branched alkyl group, a straight or branched alkenyl group, in which an alkyl or alkenyl group may be interrupted by a nitrogen or oxygen atom; an alkoxy group; a dialkylamino group; or an unsubstituted or substituted aryl group; and
R2 is a secondary amino group.
The terms xe2x80x9calkyl,xe2x80x9d xe2x80x9calkenyl,xe2x80x9d xe2x80x9calkoxy,xe2x80x9d xe2x80x9cdialkylamino,xe2x80x9d and xe2x80x9carylxe2x80x9d are as defined above.
The term xe2x80x9csecondary aminoxe2x80x9d group includes a group of the formula III: 
derived from a secondary amine R3R4NH, in which R3 and R4 are each independently alkyl, alkenyl, cycloalkyl, aryl, or, when R3 and R4 are taken together, may form a ring with the nitrogen atom and which may optionally be interrupted by a heteroatom, such as, for example, a nitrogen or oxygen atom. The terms xe2x80x9calkyl,xe2x80x9d xe2x80x9calkenyl,xe2x80x9d and xe2x80x9carylxe2x80x9d are used as defined above in forming secondary amino groups such as, for example, dimethylamino, methylethylamino, diethylamino, dialkylamino, phenylmethylamino, diphenylamino, and the like.
The term xe2x80x9ccycloalkylxe2x80x9d refers to a saturated hydrocarbon having from 3 to 8 carbon atoms, preferably 3 to 6 carbon atoms, such as, for example, cyclopropyl, cyclopentyl, cyclohexyl, and the like.
When R3 and R4 are taken together with the nitrogen atom, they may form a cyclic secondary amino group, such as, for example, piperidino, and, when interrupted with a heteroatom, includes, for example, piperazino and morpholino.
Preferred R1 groups for compounds of formula II include toluyl, e.g., p-toluyl, naphthyl, tert-butyl, dimethylamino, acetylphenyl, hydroxyphenyl, or alkoxy, e.g., methoxy. Such R1 groups when joined with a carbonyl group form an acyl group 
which preferred for compounds and formula II include toluoyl, xcex2-naphthoyl, pivaloyl, dimethylcarbamoyl, acetylsalicyloyl, salicyloyl, or alkoxycarbonyl. A preferred secondary amino group may be morpholino.
Examples of 3-acylated analogues of pyridoxal-4,5-aminal include, but are not limited to, 1-morpholino-1,3-dihydro-7-(p-toluoyloxy)-6-methylfuro(3,4-c)pyridine; 1-morpholino-1,3-dihydro-7-(naphthoyloxy)-6-methylfuro(3,4-c)pyridine; 1-morpholino-1,3-dihydro-7-pivaloyloxy-6-methylfuro(3,4-c)pyridine; 1-morpholino-1,3-dihydro-7-carbamoyloxy-6-methylfuro(3,4-c)pyridine; and 1-morpholino-1,3-dihydro-acetylsalicyloxy-6-methylfuro(3,4-c)pyridine.
The compounds of formula I may be prepared by reacting pyridoxal hydrochloride with an acyl halide in an aprotic solvent. A suitable acyl group is 
wherein R1 is as defined above. A particularly suitable acyl halide includes p-toluoyl chloride or xcex2-naphthoyl chloride. A suitable aprotic solvent includes acetone, methylethylketone, and the like.
The compounds of formula II may be prepared by reacting 1-secondary amino-1,3-dihydro-7-hydroxy-6-methylfuro(3,4-c)pyridine with an acyl halide in an aprotic solvent. An acyl group is 
wherein R1 is as defined above. A particularly suitable acyl halide includes p-toluoyl chloride, xcex2-naphthoyl chloride, trimethylacetyl chloride, dimethylcarbamoyl chloride, and acetylsalicyloyl chloride. A particularly suitable secondary amino group includes morpholino.
The compound 1-morpholino-1,3-dihydro-7-hydroxy-6-methylfuro(3,4-c)pyridine may be prepared by methods known in the art, for example, by reacting morpholine and pyridoxal hydrochloride at a temperature of about 100xc2x0 C. in a solvent. A suitable solvent includes, for example, toluene. Similarly, other secondary amines as defined for R2 may be used as reactants to prepare the appropriate 1-secondary amino compounds.
The compounds of formula I may alternatively be prepared from the compounds of formula II by reacting a compound of formula II with an aqueous acid, such as, for example, aqueous acetic acid.
One skilled in the art would recognize variations in the sequence and would recognize variations in the appropriate reaction conditions from the analogous reactions shown or otherwise known that may be appropriately used in the above-described processes to make the compounds of formulas I and II herein.
The products of the reactions described herein are isolated by conventional means such as extraction, distillation, chromatography, and the like.
Pharmaceutically acceptable acid addition salts of the compounds suitable for use in methods of the invention include salts derived from nontoxic inorganic acids such as hydrochloric, nitric, phosphoric, sulfuric, hydrobromic, hydriodic, hydrofluoric, phosphorous, and the like, as well as the salts derived from nontoxic organic acids, such as aliphatic mono- and dicarboxylic acids, phenyl-substituted alkanoic acids, hydroxy alkanoic acids, alkanedioic acids, aromatic acids, aliphatic and aromatic sulfonic acids, etc. Such salts thus include sulfate, pyrosulfate, bisulfate, sulfite, bisulfite, nitrate, phosphate, monohydrogenphosphate, dihydrogenphosphate, metaphosphate, pyrophosphate, chloride, bromide, iodide, acetate, trifluoroacetate, propionate, caprylate, isobutyrate, oxalate, malonate, succinate, suberate, sebacate, fumarate, maleate, mandelate, benzoate, chlorobenzoate, methylbenzoate, dinitrobenzoate, phthalate, benzenesulfonate, toluenesulfonate, phenylacetate, citrate, lactate, maleate, tartrate, methanesulfonate, and the like. Also contemplated are salts of amino acids such as arginate and the like and gluconate, galacturonate, n-methyl glutamine, etc. (see, e.g., Berge et al., J. Pharmaceutical Science, 66: 1-19 (1977).
The acid addition salts of the basic compounds are prepared by contacting the free base form with a sufficient amount of the desired acid to produce the salt in the conventional manner. The free base form may be regenerated by contacting the salt form with a base and isolating the free base in the conventional manner. The free base forms differ from their respective salt forms somewhat in certain physical properties such as solubility in polar solvents, but otherwise the salts are equivalent to their respective free base for purposes of the present invention.
A physician or veterinarian of ordinary skill readily determines a subject who is exhibiting symptoms of any one or more of the diseases described above. Regardless of the route of administration selected, the compounds suitable for use in methods of the invention are formulated into pharmaceutically acceptable unit dosage forms by conventional methods known to the pharmaceutical art. An effective but nontoxic quantity of the compound is employed in treatment. The compounds can be administered in enteral unit dosage forms, such as, for example, tablets, sustained release tablets, enteric coated tablets, capsules, sustained release capsules, enteric coated capsules, pills, powders, granules, solutions, and the like. They may also be administered parenterally, such as, for example, subcutaneously, intramuscularly, intradermally, intramammarally, intravenously, and other administrative methods known in the art.
Although it is possible for a compound suitable for use in methods of the invention to be administered alone in a unit dosage form, preferably the compound is administered in admixture as a pharmaceutical composition suitable for use in methods of the invention. A pharmaceutical composition comprises a pharmaceutically acceptable carrier and a compound. A pharmaceutically acceptable carrier includes, but is not limited to, physiological saline, ringers, phosphate buffered saline, and other carriers known in the art. Pharmaceutical compositions may also include additives, for example, stabilizers, antioxidants, colorants, excipients, binders, thickeners, dispersing agents, readsorpotion enhancers, buffers, surfactants, preservatives, emulsifiers, isotonizing agents, and diluents. Pharmaceutically acceptable carriers and additives are chosen such that side effects from the pharmaceutical compound are minimized and the performance of the compound is not canceled or inhibited to such an extent that treatment is ineffective.
Methods of preparing pharmaceutical compositions containing a pharmaceutically acceptable carrier and a compound suitable for use in methods of the invention are known to those of skill in the art. All methods may include the step of bringing the compound in association with the carrier and additives. In general, the formulations are prepared by uniformly and intimately bringing the compound of the invention into association with a liquid carrier or a finely divided solid carrier or both, and then, if necessary, shaping the product into the desired unit dosage form.
The ordinarily skilled physician or veterinarian will readily determine and prescribe the therapeutically effective amount of the compound to treat the disease for which treatment is administered. In so proceeding, the physician or veterinarian could employ relatively low dosages at first, subsequently increasing the dose until a maximum response is obtained. Typically, the particular disease, the severity of the disease, the compound to be administered, the route of administration, and the characteristics of the mammal to be treated, for example, age, sex, and weight, are considered in determining the effective amount to administer. Generally, a therapeutically effective amount of a compound to treat diabetes mellitus and related conditions and symptoms is in a range of about 0.1-100 mg/kg of a patient""s body weight, more preferably in the range of about 0.5-50 mg/kg of a patient""s body weight, per daily dose. The compound may be administered for periods of short and long duration.
A therapeutically effective amount of a compound for treating diabetes mellitus and related conditions and symptoms can be administered prior to, concurrently with, or after the onset of the disease or symptom. The compound can be administered to treat diabetes mellitus type I, diabetes mellitus type II, or obesity. Preferably, the compound can be administered to treat damage to blood vessels, eyes, kidneys, nerves, autonomic nervous system, skin, connective tissue, or immune system. Still preferably, the compound can be administered to treat insulin resistance or hyperinsulinemia. Also preferably, the compound can be administered to treat diabetes-induced hypertension.
Moreover, the compound may be administered concurrently with insulin and/or a hypoglycemic compound to treat diabetes mellitus and related conditions and symptoms. The compound can be administered concurrently with insulin and/or a hypoglycemic compound to treat type I diabetes, type II diabetes, or obesity. Preferably, the compound can be administered concurrently with insulin and/or hypoglycemic compound to treat damage to blood vessels, eyes, kidneys, nerves, autonomic nervous system, skin, connective tissue, or immune system. Still preferably, the compound can be administered concurrently with insulin and/or hypoglycemic compound to treat insulin resistance or hyperinsulinemia. Also preferably, the compound can be administered concurrently with insulin and/or hypoglycemic compound to treat diabetes-induced hypertension.
Typically, a compound may be administered concurrently with insulin to treat type I diabetes, type II diabetes, and related conditions and symptoms. For type II diabetes, insulin resistance, hyperinsulinemia, diabetes-induced hypertension, obesity, or damage to blood vessels, eyes, kidneys, nerves, autonomic nervous system, skin, connective tissue, or immune system, a compound may be administered concurrently with a hypoglycemic compound instead of insulin. Alternatively, a compound may be administered concurrently with insulin and a hypoglycemic compound to treat type II diabetes, insulin resistance, hyperinsulinemia, diabetes-induced hypertension, obesity, or damage to blood vessels, eyes, kidneys, nerves, autonomic nervous system, skin, connective tissue, or immune system.
xe2x80x9cConcurrent administrationxe2x80x9d and xe2x80x9cconcurrently administeringxe2x80x9d as used herein includes administering a compound suitable for use in methods of the invention and insulin and/or a hypoglycemic compound in admixture, such as, for example, in a pharmaceutical composition, or as separate compounds, such as, for example, separate pharmaceutical compositions administered consecutively, simultaneously, or at different times. Preferably, if the compound and insulin and/or hypoglycemic compound are administered separately, they are not administered so distant in time from each other that the compound and the insulin and/or hypoglycemic compound cannot interact and a lower dosage amount of insulin and/or hypoglycemic compound cannot be administered.
Suitable hypoglycemic compounds include, for example, metformin, acarbose, acetohexamide, glimepiride, tolazamide, glipizide, glyburide, tolbutamide, chlorpropamide, thiazolidinediones, alpha glucosidase inhibitors, biguanindine derivatives, and troglitazone, and a mixture thereof. Preferably, the hypoglycemic compound is tolbutamide.
A physician or veterinarian of ordinary skill readily determines a subject who is exhibiting symptoms of diabetes mellitus and related conditions and symptoms. Regardless of the route of administration selected, the compound and the insulin and/or hypoglycemic compound are formulated into pharmaceutically acceptable unit dosage forms by conventional methods known to the pharmaceutical art. An effective but nontoxic quantity of the compound and the insulin and/or hypoglycemic compound is employed in the treatment of diabetes mellitus and related conditions and symptoms. The compound and the insulin may be concurrently administered parenterally in admixture or may be concurrently administered enterally and/or parenterally separately. Similarly, the compound and the hypoglycemic compound may be concurrently administered enterally in admixture or may be administered enterally and/or parenterally separately. In some instances, the compound may be concurrently administered with insulin and a hypoglycemic compound. Such administration would involve enteral and/or parenteral administration as described above.
Parenteral administration includes subcutaneous, intramuscular, intradermal, intramammary, intravenous, and other administrative methods known in the art. Enteral administration includes tablets, sustained release tablets, enteric coated tablets, capsules, sustained release capsules, enteric coated capsules, pills, powders, granules, solutions, and the like.
A pharmaceutical composition suitable for administration includes a pharmaceutically acceptable carrier and a compound suitable for use in methods of the invention and, optionally, insulin and/or a hypoglycemic compound. A pharmaceutically acceptable carrier includes, but is not limited to, physiological saline, ringers, phosphate buffered saline, and other carriers known in the art. Pharmaceutical compositions may also include stabilizers, antioxidants, colorants, and diluents. Pharmaceutically acceptable carriers and additives are chosen such that side effects from the pharmaceutical compound are minimized and the performance of the compound is not canceled or inhibited to such an extent that treatment is ineffective.
Methods of preparing pharmaceutical compositions containing a pharmaceutically acceptable carrier and a compound suitable for use in methods of the invention and, optionally, insulin and/or a hypoglycemic compound, are known to those of skill in the art. All methods may include the step of bringing the compound and, optionally, a hypoglycemic compound in association with the carrier or additives. In general, the formulations are prepared by uniformly and intimately bringing the compound into association with a liquid carrier or a finely divided solid carrier or both, and then, if necessary, shaping the product into the desired unit dosage form.
The ordinarily skilled physician or veterinarian will readily determine and prescribe the therapeutically effective amount of the compound to treat the disease for which treatment is administered as described above.
When concurrently administering a compound with insulin and/or a hypoglycemic compound, the compound is administered in a range of about 0.1-100 mg per daily dose, typically 0.5-50 mg/kg of body weight per daily dose. A hypoglycemic compound is administered in a range of about 1 to 300 mg per daily dose, typically 1 to 200 mg per daily dose. Insulin is typically administered in a range of about 0.1 to 2 units/kg of a patient""s body weight per daily dose. A xe2x80x9cunitxe2x80x9d of insulin refers to that amount of insulin necessary to lower the blood-sugar level in a rabbit by 50% in 1 to 3 hours.